Date of Award:

8-2020

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Janice Brahney

Committee

Janice Brahney

Committee

Daniel Drost

Committee

William Doucette

Abstract

Climate change and human activities are promoting the dominance of a photosynthetic family of aquatic bacteria, cyanobacteria. Blooms of cyanobacteria are not only a visual nuisance but can produce a variety of cyanotoxins than can harm the liver, skin, and nervous system of animals and humans. We analyzed lakes in the contiguous United States and found that between 2007 and 2012, the number of lakes that produced measurable quantities of cyanotoxins increased from 33% to 45%. Nitrogen and phosphorus pollution were the main drivers of cyanobacteria blooms and toxin production between these years. Many of these lakes and reservoirs are used for crop irrigation and more frequent and toxic cyanobacteria blooms intensifies the risk of human and animal exposure to cyanotoxins through the consumption of toxic plants. We assessed how three cyanotoxins are distributed between soil, irrigation water, and lettuce plants to evaluate the exposure risk that cyanotoxins in food pose to human health. We found soil to sorb between 12 to 52% of two cyanotoxins from water, which could temporarily prevent the toxins from being taken up by plant roots and deposited into edible tissue. Also, we grew lettuce plants in a greenhouse and irrigated them with cyanotoxins. Cyanotoxins did not affect plant growth, however, we were unable to quantify the concentration of the toxins in the lettuce due to analytical limitations or that the plants were unable to sorb the toxins. Lastly, we analyzed the results from 14 published research studies on cyanotoxins in food irrigated with contaminated water. We found significant relationships between cyanotoxin concentrations in the irrigation water and those measured in plant tissues. Generally, the more cyanotoxins in the irrigation water the more cyanotoxins are measured in plants. The increase in cyanotoxin producing blooms needs to be mitigated to reduce associated health and economic risks. Management and policies should be implemented that not only mitigate the drivers of cyanobacteria and their toxins but also places limits on the acceptable concentrations in irrigation water.

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